Prestressing and reinforcing apparatus for concrete structures



y 11, 1954 H. SCHORER PRESTRESSING AND REINFORCING APPARATUS FOR CONCRETE STRUCTURES Filed N INVENTOR. /%1?M /v .S'Ewaxaee ATTORNEY.

Patented May 11,1954

UNITED STATE$ PATENT OFFICE PRESTRESSING AND REINFORGING APPA- RATUS FOR CONCRETE STRUCTURES Herman Schorer, Valhalla, N. Y., assignor to Schorer Corporation, New York, N. Y., a cor- The present invention relates to a self-contained, prestressed unit for reinforcing concrete, which unit can be embedded in the concrete similarly to conventional reinforcing bars.

Reinforcing units have been proposed which comprise a central compression member and a plurality of tension wires wound in opposite directions helically around the central compression member and being spaced therefrom. Special anchorages are provided at both ends of the compression member. The tension members are connected to the anchorages in such a way that they can be tensioned, and the tension reaction force is simultaneously transferred to the compression member for stressing the unit.

Upon hardening of the concrete, the stress in the compression member can be gradually released, whereby the corresponding reaction is transmitted to the concrete in the form of an internal compression force. The transfer of this force to the concrete may be accomplished either by the bond resistance of the helically arranged, comparatively thin tension members, the bearing pressure of the spacer discs, or the sliding resistance of the end members, or the combined action of these resistances.

For reasons of economy, it will generally not be advisable to embed the end members previously described in the concrete. By locating these end members outside of the face of the concrete,

it will be possible to cut the tension members near the face of the concrete and thereby recover and re-use the end members. This procedure, of course, prevents the end member from functioning as a permanent end anchorage of the tension members. Numerous tests indicate the feasibility, provided that the size of the tension members does not exceed certain limits.

However, the protruding end members also make it necessary to provide holes in the concrete forms or molds, which is not desirable for reasons of economy.

Furthermore, the individual tension members, spacers, and the tubular enclosure of the compression member complicate the manufacture of the unit and represent, to some extent, additional cost items for material required.

It is the object of the present invention to provide an improved prestressed reinforcing unit for concrete which retains the basic principles of construction and operation of conventional units having a longitudinal compression member and longitudinal or helically wound tension means, but which eliminates the disadvantages listed above. The unit according to the invention is characterized by the following improvements:

1. The end members are designed to serve as permanent anchors, to be embedded in the concrete. They consist of a longitudinal rough body, provided with a plurality of radially projecting longitudinal toothed ribs and radially projecting lugs or hooks. The extent of the radial projection of the toothed ribs is greater at the outer end of the body than at the end from which the compression member projects into the concrete. The core of the end member is hollow and designed to receive a removable holding device, such as a set screw. This holding device is provided with a longitudinal cavity for receiving the end of the compression member. A steel ball may be inserted in this cavity for reducing frictional resistance when the set screw is tightened against the end of the compression member. The steel ball also assures centric application of the compressive force which is applied to the compression member by means of the recessed holding device when the unit is stressed.

The end member is also provided with a clamping device for securely fastening the ends of the tension members.

2. The longitudinal tension members consist of one or more continuously wound wires having adjacent lengths along the compression member to form a tube therearound whose wall is formed by parallel wires, the compression member serving as mandrel during the winding operation. The number and diameter of the wires forming the parallel wire tube are so chosen as to provide a space between the wire tube and the encased longitudinal compression member for facilitating removal of the latter. The parallel portions of the wires are pressed together to form a solid tube by means of a wrapping wire, which forms a continuation of the parallel wire system and is wound tightly around the wire tube.

The longitudinal wires are looped over the projecting lugs of the end members. The starting end and the terminal end of the helical wrapping wire is wound around the end member, one end on each end member, the wire being laid in the gaps between the teeth of the toothed ribs. The end of the wrapping wire is finally fastened by means of the clamping device at one of the end members.

3. The stressing of the reinforcing unit is accomplished by tightening the holding device (set screw) at one or both end members. The resulting compressive force is transmitted to the wire tube system, which closes any gap that may J exist between the adjacent parallel wires. Tests have shown that a truly motor-tight wire tube is thereby obtained. Since the minimum inside diameter of the tightly closed wire tube is somewhat larger than the maximum diameter of the compression member, the resistance to the subsequent removal of the compression is relatively small.

4.. The stability and safety of the improved prestressed reinforcing unit is greatly superior to that of conventional units.

Furthermore, the helical wrapping wire is relatively longer than the parallel wires. Since the total elastic elongation is identical for both wires, it follows that the wrapping is subjected to a relatively smaller tensile stress. This means that the highly stressed longitudinal wires are protected by a relatively safer system of outside wires.

5. The bond resistance of the improved prestressed reinforcing unit is greatly increased by the tight helical wrapping wires, which, combined with the parallel wires produce an effect similar to that of a threaded rod. The bond resistance of the parallel wires is further increased by subsequent pressure grouting of the tubular inside space upon removal of the compression rod. The entire stressed wire system thus becomes thoroughly embedded in concrete and mortar, giving effective protection against corrosion and fire hazards.

Further and other objects of the present invention will be hereinafter set forth in the accompanying specification and claims, and are shown in the drawings which, by way of illustration, show What I now consider to be preferred embodiments of the invention.

In the drawings:

Fig. 1 is a plan view of a unit according to the invention;

Fig. 2 is a large scale cross-sectional view of a unit according to the invention, the section being taken along line IIII of Fig. 1;

Fig. 3 is a longitudinal sectional view of an end assembly according to the invention, without the tension members;

Fig. 4 is a cross-sectional view of the end assembly shown in Fig. 3, the section being made along line IV-IV of said figure;

Fig. 5 is a cross-sectional view of the end assembly shown in Fig. 3, the section being made along line V--V of said figure;

Fig. 6 is a cross-sectional view of the end assembly shown in Fig. 3, the section being made along line VIVI of said figure;

Fig. 7 is a top end view of the end member shown in Figs. 3 to 6;

Fig. 8 is a side elevation of a modified holding device according to the invention;

Fig. 9 is a diagram illustrating how the tension member is arranged on a unit according to the invention.

Like parts are designated by like numerals in all figures of the drawings.

Referring more particularly to the drawings, numerals I and 2 designate the end members or devices of a unit according to the invention, to which tension members ID are secured. These end devices comprise a body 3 having a threaded bore 4. A threaded protrusion 9 projects radially from body 3 and has an axial slot for receiving the starting end or the terminal end of the tension means. The tension means are securely held in the slot of the protrusion 9 by a nut screwed thereon. Lugs 5, 6, 1, and 8 project radially from and are regularly distributed around the central portion of body 3. At least one of the lugs, 8 on the member illustrated, is axially ofiset with respect to the other lugs. The end of each lug has a recess extending across the lug at a right angle to the longitudinal axis of member I. The tension members are looped over the lugs, and the recesses across the ends of the lugs are for receiving an end portion of the tension members when the portion is wound around the body 3 and around the longitudinal portions of the tension members forming return-bends on the lugs. The diameter of the end of body 3 extending to the tube formed by the adjacent, longitudinal, and parallel portions of the tension members H1, is smaller than the diameter of the portion of the body which is distal from said tube. The portion of the body 3 between the lugs 5, 6, I, 8 and the end of the body which is proximal to the tube formed by the tension members I0 is conical and tapers from the lugs to the end. This tapering portion has axial ribs or fins l I, l2, 13, I4 radially projecting therefrom. The ribs l2 and [4 have five teeth each and ribs l l and l 3 two teeth each for fixing the position of the ends of the tension members it: which are Wound helically around the end members. The teeth on ribs II and 13 are offset with respect to one another to facilitate helical winding of the end portions of the tension members.

Screwed into the threaded bore 4 of the body member 3 is a holding device formed as a longitudinal plug 15 having a longitudinal bore or cavity l6 for receiving a compression member 11. Bore i6 is separated from a hexagonal cavity [8 at the outer end of the plug by an internal shoulder [9. A steel ball 20 is inserted between the end of compression member ll, which is a steel rod, and shoulder IS. The hexagonal cavity I8 is for inserting a suitably shaped key for turning plug [5 in body member 3. If plug I5 is screwed into body member 3, the tension members III, which are substantially parallel to the compression member H, are tensioned, and the tension reaction is transmitted by the end device 3, l5 and particularly by the threads in bore 4 and the corresponding threads on the plug means [5 to the latter and therefrom to the member IT.

The diameter or" the longitudinal bore in body 3 is reduced at the small diameter end of the body to substantially the same diameter as that of the bore IS in plug l5 for providing a guide for the end of member ll.

Fig. 8 illustrates an alternative holding means having a square head instead of a polygonal cavity for applying a key or wrench.

Diagram Fig. 9 shows an arrangement of Winding and looping a tension member, which in most cases will be a steel wire, to complete the prestressing unit according to the invention. For the purposes of illustration and clarity, Fig. 9 represents the structure of the assembly of Fig. 1 with the lugs and ribs shown in common planes. The starting end 2| of the wire is inserted in the slot of protrusion 9 of end member I slipped over one end of compression rod H. The wire accuse is'securely held in the slot by a nutzscrewed on the protrusion 9. The wire is then wound several' times around athroat portion 22 ofbody 3- before being laid on lug 8-, from which it extends to a lug on end member '2 at the other end of compression rod II. It is looped over the lug, for example I, of member 2 and returned to lug I of end memberl over which. it: is looped to bereturned to lug 8 of member 2, from whichupontha wire COllliiIlllGSg substantially helically' around the; conical. portion. of member I toward the small diameter end thereof, the windings being held in proper position by laying the wire in suitable gaps between the teeth on the ribs of member I. After leaving the last gap, the wire is wound in helices around the tube formed by the adjacent longitudinal portions of the wire along rod I7. The helices may be made more or less steep to answer different requirements. The diameter of the tube formed by the adjacent longitudinal wire portions depends on the number of wire portions extending along rod I1 and their diameters. After the wire has been wound around the wire tube and has reached end member 2, the wire is laid in a gap between two outermost teeth of a rib of body member 3 of the end member or unit 2. The wire is then wound in helices around the conical part of member 2, the gaps between the teeth on the ribs of said member serving to fix the helices in the desired positions. The end portion 23 of the wire leaving the last tooth gap is subsequently laid into the recesses across the ends of the lugs on member 2, first into the recess of lug 8, then into that of lug 5, then into that of lug 6, and then into that of lug I. Thereupon the wire is wound several times around the throat or cylindrical portion of end member 2, and the end of the wire is clamped into the slot of projection 9 of member 2.

For prestressing the unit, the holding device I5 of at least one end member is screwed into body 3, whereby the distance between the bodies 3 is increased, the distance between members I5 being fixed by the compression rod I1, and the wire I6 is stretched. Ball 20 reduces friction and thus facilitates tighening of plug I5 in body 3. The unit is inserted in the mold in prestressed condition or is stressed after it is placed in the mold. The concrete can now be poured and will bind on the wire I without penetrating the wire tube and without coming in contact with the compression member I'I. After the concrete has hardened, plug I of one or both end members can be unscrewed from its body 3, whereby tension on the wire In is released causing it to shrink, and the concrete adhering to the wire is compressed. Plug I5 may be completely removed and rod I? pulled out if desired, leaving a hole in the concrete which may serve for draining water or for other purposes, or which may be filled with grout.

While I believe the above described embodiments of my invention to be preferred embodiments, I wish it to be understood that I do not desire to be limited to the exact details of method, design and construction shown and described, for

lbs.

61 obvious modifications will occur to a person skilled in the art.

I claim:

I. A self-contained prestressing mechanism for concrete comprising arodlike compression member, a plurality of wirelike tension members. spaced from and disposed substantially parallel to and. around said compression member, awrapping wire helically wound around said tension membersin helixes' forming axially spaced windings, and a stressing device disposed: at: either end of said mechanism and abutting. against the end of said compression member-and being firmly connected to said tension members andto said wrapping wire, said stressing devices. comprising means for simultaneously tensioning said tension members and said wrapping, wire and compressing said compression member and pulling said wrapping wire radially against said tension members to press the latter laterally against each other to form a tight tube at all stress conditions of the mechanism.

2. A reinforcing unit for concrete comprising a longitudinal compression member, opposed end devices disposed at each end of said compression member, a plurality of longitudinally extending tension means disposed in a circumferential series about and completely around said compression member, said tension means being in sideby-side engaging relationship and forming a sheath around said compression member and spaced therefrom, a wrapping wire wound around said tension means in axially spaced helixes, said end devices individually abutting a ainst the ends of said compression member and being firmly connected to said tension means and to said wrapping wire and comprising means for simultaneously tensioning said tension means and said wrapping wire and compressing said compression member and pulling said wrapping wire radially against said tension means for maintaining side-by-side engagement of the latter at all stress conditions of the unit.

3. A reinforcing unit for concrete comprising a longitudinal compression member, opposed end devices disposed at each end of said compression member, a continuous tension means extending between said end devices, the ends of said tension means being fixed to said end devices, an intermediate portion of said tension means extending alternately from one of said end devices to the other of said end devices and interconnecting said opposed end devices, there being longitudinally extending lengths of said intermediate portion disposed in a circumferential series about and completely around said compression member, said lengths being in side-by-side engaging relationship and forming a sheath around said compression member and spaced therefrom, and other intermediate portions of said continuous tension means spirally surrounding and engaging said lengths.

4. A reinforcing unit for concrete comprising a longitudinal compression member, opposed end devices disposed at each end of said compression member, each end device comprising a longitudinal body element having a longitudinal bore and longitudinally displaceable means therein, a cavity in each of said displaceable means, the ends of said compression member being disposed in the cavities of the displaceable means and the end faces of said compression member bearing on the bases of said cavities, a plurality of lugs positioned on the outer surface of each end device and in radial relation thereto, a plurality of longitudinally extending fins disposed on the outer surface of each end device and in radial relation thereto, the outer surface of-each fin having transverse notches thereon, a continuous tension rneans extending between said end devices, the ends of said tension means being fixed to said end devices, an intermediate portion of said tension means extending alternately from the lugs on one of said end devices to and around the lugs on the other of said end devices and interconnecting said opposed end devices, there being longitudinally extending lengths of said intermediate portion disposed in a circumferential series about and completely around said compression member, said lengths being in side-by side engaging relationship and forming a sheath around said compression member and spaced therefrom, other intermediate portions of said tension means spirally enveloping the outer surface of said end devices and engaging the notches of said fins, and other intermediate portions of said continuous tension means spirally surrounding and engaging said lengths.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 716,555 King Dec. 23, 1902 2,270,240 Freyssinet Jan. 20, 1942 2,303,394 Schorer Dec. 1, 1942 2,328,033 Schorer Aug. 31, 1943 2,449,276 Chalos Sept. 14, 1948 FOREIGN PATENTS Number Country Date 221,529 Switzerland Aug. 17, 1942 

